Substituted N-thiomethylphenothiazines as lubricant stabilizers

ABSTRACT

Lubricants stabilized against oxidative degradation by the incorporation therein of N-thiomethylphenothiazine derivatives, as well as certain phenothiazines within the indicated group.

This application is a continuation of application Ser. No. 315,257,filed Feb. 21, 1989, now abandoned, which is a continuation of Ser. No.948,272, filed Dec. 31, 1986, now abandoned.

This invention relates to lubricant compositions which are stabilizedagainst oxidative degradation by the presence therein of certainN-thiomethylphenothiazine derivatives. It also relates to a number ofnovel phenothiazines within the broader group.

It is known to stabilize lubricants by the addition of antioxidantssuch, for example, as sterically hindered phenols, derivatives ofp-phenylene diamine or of di-phenylamine in order to avoiddecomposition, sludge formation, viscosity increases, and the like. U.S.Pat. No. 3,535,243 also discloses the use of diaminonaphthalenes asantioxidative additives for ester lubricants, while U.S. Pat. No.3,536,706 discloses N-unsubstituted phenothiazines for a similarpurpose.

It has now been discovered that certain derivatives ofN-thiomethylphenothiazine show surprisingly high stabilizer activity andsufficient solubility in a broad range of mineral and synthetic oils.Thus, the subject matter of the instant invention is a lubricantcomposition comprising mineral oils, synthetic oils, mixtures thereof,and the like, and an antioxidative compound corresponding to the formula##STR1## wherein R₁ are independently hydrogen, alkyl of 1 to 24 carbonatoms, cycloalkyl of 5 to 7 carbon atoms or aralkyl of 7 to 9 carbonatoms;

A and A' are independently alkylene of 1 to 8 carbon atoms;

n is 0 or 1; and

R₂ is alkyl of 1 to 18 carbon atoms, cycloalkyl of 5 to 7 carbon atoms,said cycloalkyl substituted by alkyl of 1 to 18 carbon atoms, phenyl,phenyl substituted by alkyl, alkoxy or thioalkyl to a total carbon atomcontent of 7 to 30, naphthyl or naphthyl substituted by alkyl, alkoxy orthioalkyl to a total carbon atom content of 11 to 40.

Alkyl groups within the indicated definitions may be straight-chain orbranched and may be methyl, ethyl, propyl, isopropyl, n-butyl, isobutyl,n-hexyl, n-octyl, 2-ethylhexyl, n-decyl, n-dodecyl, n-octadecyl orn-eicosyl. Cycloalkyl may be cyclopentyl or cyclohexyl. Aralkyl may bebenzyl, α-methylbenzyl or α,α-dimethylbenzyl.

Alkylene groups include methylene, propylene, hexylene or octylene, butpreferably correspond to the formula ##STR2## wherein R₃ is alkyl of 1to 7 carbon atoms.

Preferred compounds include those wherein R₁ are independently hydrogenor alkyl of 1 to 12 carbon atoms; A and A' are independently ##STR3##and R₂ is alkyl of 4 to 12 carbon atoms or phenyl or phenyl mono- or di-or trisubstituted by alkyl of 1 to 8 carbon atoms or with one of thesubstituents being alkoxy or thioalkyl of 1 to 12 carbon atoms.

The N-thiomethylphenothiazine compounds may be prepared by reactingphenothiazine, formaldehyde and the appropriately substituted mercaptanor thiophenol in the presence of an alcoholic solvent such as methanoland ethanol at reaction temperatures ranging from 25° to 200° C. Thevarious starting materials needed to prepare the indicated compounds areitems of commerce or can be prepared by known methods.

The lubricant may be an oil or a grease based on mineral or syntheticoils, these lubricants being well known to those skilled in the art. Theterm mineral oil includes all mineral oils used for lubricant purposes,such as hydrocarbon mineral oils. The synthetic oil may be, forinstance, an aliphatic or aromatic carboxylic ester, a polymeric ester,a polyalkylene oxide, a phosphoric acid ester, polyalphaolefins, or asilicone. Greases may be obtainable from these by adding metal soaps orsimilar thickeners.

The amount of phenothiazine compound added to the lubricant depends onthe sensitivity of the oil base to oxidation and on the desired degreeof protection. Generally, 0.01 to 2% by weight will be added, andpreferably 0.05 and 0.5%. The compounds may be used in combination withother antioxidants known as oil additives. Examples thereof are aromaticamines such as p-tert.octylphenyl-α-naphthylamine,p,p'-di-tert.octyldiphenylamine,2,3-dihydro-3,3-dimethyl-4H-1,4-benzothiazine, phenothiazine,diphenylamine, N-allylphenothiazine, N-allyldiphenylamine orphenyl-α(β)naphthylamine; hindered phenols such as neopentanetetrayltetrakis(3,5-di-tert-butyl-4-hydroxyhydrocinnamate), n-octadecyl3,5-di-tert-butyl-4-hydroxyhydrocinnamate,1,3,5-trimethyl-2,4,6-tris-(3,5-di-tert-butyl-4-hydroxybenzyl)benzene,1,3,5-tris-(3,5-di-tert-butyl-4-hydroxybenzyl)isocyanurate,2,6-di-tert-butyl-p-cresol or2,2'-ethylidene-bis(4,6-di-tert-butylphenol; aliphatic or aromaticphosphites; esters of thiodipropionic or thiodiacetic acid; or salts ofdithiocarbamic or dithiophosphoric acids.

Such antioxidant combinations may show a synergistic action, i.e., thestabilizing effect of such a mixture being greater than the sum of theperformances of the individual antioxidants. Such synergisticperformance can be obtained when combining the instant compounds withcertain aromatic amines or hindered phenols or with both types ofantioxidants.

The lubricant composition may also contain other additives, such asmetal-passivating agents including 5,5'-methylene-bisbenzotriazole,4,5,6,7-tetrahydrobenzotriazole and 2,5-dimercaptothiadiazole; rustinhibitors; viscosity regulators including polyacrylates, polybutenes,polyvinylpyrrolidones and polyethers; pour point depressants; dispersingagents; detergents; or extreme pressure/anti-wear agents includingtriphenyl phosphorothionates, diethanolaminomethyl tolyltriazole anddi(2-ethylhexyl)aminomethyl tolyltriazole; said additives being widelyknown and used in lubricants.

Phenothiazine compounds within the generic formula wherein R₂ is alkylhave been previously disclosed. For example, U.S. Pat. No. 3,494,885discloses N-substituted phenothiazines wherein the N-substitution is C₂-C₁₈ alkylenethioalkyl for use as antioxidants in polycarbonates andpolyesters. Similarly N-alkylenethioalkylphenothiazines have beendisclosed in Winthrop et al, J. Am. Chem. Soc., 80, 4331-33 (1958) for apharmacological utility.

Accordingly, the novel phenothiazines forming part of the instantinvention correspond to the above noted generic formula with theexception that the R₂ definition does not include alkyl. The preferredsubstituents are also as defined above, excepting R₂ as alkyl, and themethods of preparation are, of course, as described hereinabove.

Compounds of this invention are also effective in stabilizing otherorganic materials such as plastics, polymers and resins in addition tothe mineral and synthetic fluids.

Substrates in which the compounds of this invention are particularlyuseful are polyolefins such as polyethylene and polypropylene,polystyrene, including impact polystyrene, ABS resin, SBR, isoprene, aswell as natural rubber; polyesters including polyethylene terephthalateand polybutylene terephthalate, including copolymers.

These stabilized polymer compositions may optionally also containvarious conventional additives such as antioxidants including alkylatedmonophenols, alkylated hydroquinones, hydroxylated thiodiphenyl ethers,alkylidene-bisphenols, various benzyl compounds, acylaminophenols andesters and amides of hindered hydroxyphenyl propionic acids; UVabsorbers and light stabilizers including hydroxyphenyl benzotriazoles,benzophenones, benzoic acid esters, acrylates, nickel compounds,sterically hindered amines and oxalic acid diamides.

The following examples will further illustrate the embodiments of theinstant invention.

EXAMPLE I N-(Phenyliomethylene)phenothiazine

Phenothiazine (19.9 grams, 0.100 mol) is dispersed in 150 ml of ethanoland benzenethiol (11.4 grams, 0.101 moles) is added to the dispersionfollowed by 37.4% formaldehyde (8.9 grams, 0.111 moles).

The dispersion is heated for 24 hours, further heating indicating thatno additional reaction is taking place. The solvent is removed bydistillation at 20 mm Hg pressure and unreacted benzenethiol removed atreduced pressure. The residue (28 grams) is crystallized successivelyfrom n-heptane, and a mixture of ethanol-cyclohexane yielding a total of14.6 grams (45% yield) of the desired product as white crystals.

Anal. Calcd. for C₁₉ H₁₅ NS₂ :C, 70.99; H, 4.70; N, 4.36. Found: C,70.8; H, 4.7; N, 4.3

EXAMPLE II N-(n-Octylthiomethylene)phenothiazine

Formaldehyde (37 wt. %, 6.9 grams, 0.111 moles) is added to a dispersionof phenothiazine (19.9 grams, 0.100 moles) in 250 ml. of methanol,n-Octyl mercaptan (15.0 grams, 0.100 moles) is then added and themixture stirred at reflux for about 30 hours. The solvent is removed atreduced pressure and the resulting residue dissolved in 400 ml oftoluene and washed with water and dried over sodium sulfate. The driedtoluene solution is freed of solvent under pressure with the residuebeing dissolved in 150 ml of refluxing n-heptane and allowed to cool toroom temperature. Thin layer chromatography shows the crystallineprecipitate (6.8 grams) to be phenothiazine. Removal of the heptane bydistillation of the n-heptane under vacuum yields 25.6 grams of a brownresidual liquid. This residual liquid is purified by High PressureLiquid Chromatography, yielding 18.2 grams of yellow liquid (51% yield).

Anal. Calcd. for C₂₁ H₂₇ NS₂ : C, 70.54; H, 7.61; N, 3.92; S, 17.93.Found: C, 70.4; H, 7.9; N, 4.1; S, 17.8

EXAMPLE III N-(Benzylthiomethylene)phenothiazine

The compound of Example III is prepared by following the generalprocedure of Example I and reacting benzylthiol with formaldehyde andphenothiazine.

EXAMPLE IV N-(4-Tert-butylphenylthiomethylene)phenothiazine

The compound of Example IV is prepared by following the generalprocedure of Example I and reacting 4-tert-butylthiophenol withformaldehyde and phenothiazine.

EXAMPLE V N-(2,4-Dimethylphenylthiomethylene)phenothiazine

The compound of Example V is prepared by following the general procedureof Example I and reacting 2,4-dimethylthiophenol with formaldehyde andphenothiazine.

EXAMPLE VI N-(4-Methoxyphenylthiomethylene)phenothiazine

The compound of Example VI is prepared by following the generalprocedure of Example I and reacting 4-methoxythiophenol withformaldehyde and phenothiazine.

EXAMPLE VII N-(2-Naphthylthiomethylene)phenothiazine

The compound of Example VII is prepared by following the generalprocedure of Example I and reacting 2-naphthylmercaptan withformaldehyde and phenothiazine.

EXAMPLE VIII Engine Oil Thin Film Oxygen Uptake Test

This test is conducted in a standard rotary bomb apparatus (described inASTM D-2272) with modifications in procedure as described in thePreprint No. 82 CC-10-1, presented at the Conference of the AmericanSociety of Lubrication Engineers, Oct. 5-7, 1982.

A 1.5 ml. test sample of 150 N paraffinic mineral oil containing enoughzinc dialkyldithiophosphate (ZDTP) to give 0.1% by weight of zinc and0.5% by weight of the test compound is placed in the test apparatus. Tothe above is added a catalyst package comprising 0.075 grams of oxidizedfuel components, 0.075 grams of soluble metal catalyst* and 0.030 gramsof water. The temperature is set at 160° C and the initial oxygenpressure is 90 psi (620 kPa). Failure is taken as the time in minutesfor a pressure drop of 25 psi (172 kPa) to be observed. The test resultsare given below.

    ______________________________________                                        Test Compound  Failure                                                        of Example     Time (minutes)                                                 ______________________________________                                        Base oil       99-105                                                         I              138                                                            II             145                                                            ______________________________________                                    

The data thus show a significant improvement in stability towardoxidation when the instant compounds are added to oil.

In summary, this invention provides a novel class of lubricantantioxidants which exhibit excellent antioxidative performance.Variations may be made in procedures, proportions and materials withoutdeparting from the scope of the invention as defined in the followingclaims.

What is claimed is:
 1. A lubricant composition consisting essentially ofa mineral oil or a synthetic oil or mixtures thereof and an effectivestabilizing amount of a compound of the formula ##STR4## wherein R₁ areindependently hydrogen, alkyl of 1 to 24 carbon atoms, cycloalkyl of 5to 7 carbon atoms or aralkyl of 7 to 9 carbon atoms;A is methylene andA' are independently akylene of 1 to 8 carbon atoms; n is 0 or 1; and R₂is alkyl of 1 to 18 carbon atoms, cycloalkyl of 5 to 7 carbon atoms,said cycloalkyl substituted by alkyl of 1 to 18 carbon atoms, phenyl,phenyl substituted by alkyl, alkoxy or thioalkyl to a total carbon atomcontent of 7 to 30, naphthyl or naphthyl substituted by alkyl, alkoxy orthioalkyl to a total carbon atom content of 11 to
 40. 2. The lubricantcomposition of claim 1, wherein R₁ are independently hydrogen or alkylof 1 to 12 carbon atoms.
 3. The lubricant composition of claim 1,wherein A' is independently ##STR5## wherein R₃ is alkyl of 1 to 7carbon atoms.
 4. The lubricant composition of claim 1, wherein R₂ isalkyl of 4 to 12 carbon atoms, phenyl or phenyl mono-, di- ortrisubstituted by alkyl of 1 to 8 carbon atoms or one of saidsubstitutents being alkoxy or thioalkyl of 1 to 12 carbon atoms.
 5. Thelubricant composition of claim 1, wherein said compound isN-(phenyliomethylene)phenothiazine.
 6. The lubricant composition ofclaim 1, wherein said compound is N-(n-octylthiomethylene)phenothiazine.